Deflexion typically involves the loss of some inflectional affixes, notably affecting word endings to indicate noun cases and verbal tenses. This is part of a process of gradual decline of the inflectional morphemes, defined as atomic semantic units bound to abstract word units (lexemes). Complete loss of the original subset of affixes combined with a development towards allomorphy and new morphology is associated with the formation of pidgins and creole languages.
Deflexion is a common feature of the history of many Indo-European languages. According to the Language Contact Hypothesis for Deflexion, supported by the comparison between Germanic languages, for instance, Icelandic and Afrikaans, this process is attributed to language contact. Specifically, the phenomenon occurs in the presence of large, influential groups of speakers that have acquired the leading idiom as a second language (L2 acquisition), thus by nature is limited to economical trade-offs widely considered as acceptable. Though gradual, English experienced a dramatic change from Old English being a moderately inflected language using a complex case system, to Modern English, considered a weakly inflected language or even analytic. Important deflexion changes first arrived in the English language with the North Sea Germanic (Ingvaeonic) shifts, shared by Frisian and Low German dialects, such as merging accusative and dative cases into an objective case. Viking invasions and the subsequent Norman conquest accelerated the process. The importance of deflexion in the formative stage of a language can be illustrated by modern Dutch, where deflexion accounts for the overwhelming majority of linguistic changes in the last thousand years or more. Afrikaans virtually originated from Dutch by deflexion. French is another example of a language where deflexion has been exceptionally strong.
According to the unidirectionality hypothesis, deflexion should be subject to a semantically driven one-way cline of grammaticality. However, exceptions to the gradual diachronic process have been observed where the deflexion process diminished or came to a hold, or where inflexional case marking was occasionally reinforced.